Even the feds (and most professional PD's)knock before entering, and ID themselves before knocking down the door, even SWAT teams.
I was assigned to a Fed task force for a couple of years, they knock and wait for about 5 seconds and then go in. Is that knocking?
I know many feds and not all are as wholesome and professional as you think. The old adage, absolute power corrupts absolutely, the feds are more powerful than any state or local agency and have better resources. One of the most powerful people around is a U.S. attorney and his/her power to indict and sieze property on very slim evidence.
I do not recall a big discussion when they were after the mob bosses and listening to their phones and kicking in their doors or todays terrorists. I guess it ws okay then, right?